Heretofore in conventional presses for single operation or with progressive dies, there is normally employed a bed, a reciprocal slide, a power drive for the slide and apparatus for feeding a stock strip onto the dies on the bed. Normally, the outer edges or some portion of the strip remains intact longitudinally and moves the parts from station to station through final forming. A die set including a die or plurality of longitudinally spaced progressive dies are mounted upon a lower disc shoe and secured to the bed. There is a corresponding punch for each die secured to the upper shoe and connected to the reciprocal slide. Conventional feed means are provided for positioning the stock in the die and for removing the formed articles after a number of reciprocations of the punches and intermittent advances of the stock. These presses are very expensive and can range $150,000 to $800,000 new.
Heretofore there has also been employed transfer presses which alone are similarly expensive and include a die set having a series of longitudinally spaced sequential dies secured upon the lower die shoe and anchored to the bed, and a corresponding series of punches secured to the reciprocal side, together with a transfer mechanism built into the press for intermittently moving the respective workpieces from one station to the next. This press cannot perform the motion and functions of conventional presses and range in cost 25%/50% more than conventional press new.
Heretofore for progressive dies used in a conventional press, after a series of incremental feed movements of the strip of stock and reciprocations of the punches, the finally formed part is separated from the feed strip of stock and ejected, with additional successive formed parts separated from the feed strip after the last forming and ejected. Additional successive formed parts are separated after the last forming in a continuous operation.
There are certain types of work that cannot be properly formed in the conventional press employing progressive dies. These are parts normally that have increased transverse dimensions in the shoulders and can only be formed in a transfer press.
In such type of work, a transfer press is used, i.e., a completely different press. Here blanks are individually delivered to the first die station. After a first punching operation, with all of the punches retracted, a transfer mechanism is employed to grip the workpiece or a series of partly formed workpieces and simultaneously move it or them to the next adjacent station ready for the next downward movement of the corresponding punch and to disengage from the workpiece. Unlike progressive dies in a conventional press, there is no continuous work supporting strip which continuously moves over the dies. Transfer presses can only do one job for a particular workpiece with a plurality of sequential formation therein and wherein there is a predetermined pitch or distance between work stations. For a different workpiece and a different pitch distance, there is required the removal of all of the drive apparatus which is usually a permanent part of the transfer press at its opposite ends as well as specific transfer apparatus at the intermediate die space. All of this must be done before the transfer press has added thereto a new die set for a different product and possibly for a different pitch. Such a change normally takes four men working all day for a week. This includes modification of mechanical parts, the electrical parts, the air control parts and the switches. Once a transfer press has been tooled for a particular job, it is highly expensive and time consuming to modify such press for different tooling or dies.